How does a person figure a bid for sheetrock finish and painting?

My brother has been doing sheetrock and painting work, mostly residential and bids the jobs by going in and measuring each wall space that he has to do. He has the chance to do 4 commercial jobs, finish the sheetrock and paint, each between 20,000 to 40,000 sq ft but can't figure out if he's supposed to bid on the floor space sq footage or the wall space sq footage. This could be his chance to really get going on his own and he's afraid of not bidding right, but we already know that a bid of 1.00 a sq foot is expected, just not if that means the sq footage of floor space or wall space. I hope this makes sense and someone can help really soon.

This most likely would be floor space. That way all bids come in from other trades in a similar and comparable format. For example: assume an electrition putting in a bid. He (or she) wouldn't be able to fiqure out by sq. ft since he is really dealing in feet of wire laid. A carpet installer would be floor footage, ductwork at yet a different scale.

So, by having all trades bid at per floor square footage everyone is putting their bid's in at the same level.

well if he cant figure it out then maybe he shouldnt bid it. I only say that because if he is not knowledgaeable in the field than he could put himself in a bad situation. Theres no reason why he cant bid it the same way he would as residential altho the labor rate would typically be higher for commercial work. If he has not looked at the space and would like to he needs to find out if there will be a job walk and attend it or request permission from whomever is requesting the quote that he could go look at the space.